The FiveLeg Circular Intersections Controlling Coordination Model五叉环岛交通模型.docx
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TheFiveLegCircularIntersectionsControllingCoordinationModel五叉环岛交通模型
TheFive-LegCircularIntersectionsControllingCoordinationModel
JiaSusu
115120910046
X_03
DingYaping
Master’sDegree
AntaiCollegeofEconomics&Management
2015/12/26
TheFive-LegCircularIntersectionsControllingCoordinationModel
Abstract
Roundaboutsarecircularintersectionswithspecificdesignandtraffic-controlfeatures.Andappropriatesignalphasessettingcanpartlysolvetheconflictandweavingsituationcausedbytheinandoutroundaboutflows.Thispaperaimstoproposeamethodologyforthetraffic-signalcontrollingofafive-approachcircularintersections,namelyaroundaboutwithfiveapproaches.Amodelofparameteroptimizationfortraffic-signalcontrollingbasedontheconstraintofthecirculatoryroadwaycapacityispresentedtohelprelievethecongestioninmodernroundabouts.Thismodeltakestwomainpointsintoconsideration,thecapacityconstraintandthegreenandredsignalcontrollingcoordinationbetweentheapproachesandcirculatoryroadwaystrafficlights.AsimulationwithVISSIMsoftwareispresentedinthethirdchaptertoprovetheeffectivityoftheoptimization.TheresultshowsthatthemethodologyproposedinthispaperissuccessfullyappliedtotheOpticValleyroundaboutinWuhan,Chinaandtheimprovementisapparent.
KeyWords:
Five-legroundabout;CirculatingLaneCapacity;SignalCoordination
1.Introduction
Thefeaturesofroundaboutincludeyieldcontrolofallenteringtraffics,channelizedapproaches,andappropriategeometriccurvaturestoensurethattravelspeedsonthecirculatoryroadwayaretypicallylessthan50km/h(Hagring,2001).ThemodernroundaboutwasdevelopedintheU.K.in1960sandmodernroundaboutsprovidesubstantiallybetteroperationalandsafetycharacteristicsthanoldertrafficcirclesandrotaries(Hallworth,1992).Therefore,manycountrieshaveadoptedthemasacommonintersectionform.
Roundaboutshaveuniquecharacteristicsthatwarrantconsiderationbydevelopersandmanagersoftheroadsystem(Garber&Hoel,2008).However,aroundaboutusuallyhasmorethanonelaneontheroadwayinordertoincreasethecapacity.Andthemulti-lanesbringaboutconflictpointsandweavingsectionswhichhavetobeeliminatedinordertokeepsmoothandsafeoperationoftheroundabout.
Thebottlenecksofaroundaboutwithtwoormorecirculatorylanesaretheweavingsections,wherethevehiclesenterorleavetheroundabout.Disorderwilloccur,causingserioussafetyproblemifthereisnotraffic-signalcontrol.Andthedesignedcapacitycannotbeachieved.
Theroundaboutswithoutsignalcontrollingareeasytobeinfluencedbythecapacityofcirculatoryroadways,asaresult,whenthetrafficflowsintheapproachesdrawnearorevenexceedtheweavingcapacityofthecircularintersections,gravelyseriouscongestionwouldoccurandsometimesitcanevencause“dead-lock”(Hagring,Rouphail&Sørensen,2003).Consequently,theupstreamapproacheswillalsobeblockedup.
Comparedwiththefour-approachroundaboutswithouttrafficsignalcontrol,theweavingsectionswithtrafficflowsofdifferentdirectionsinthefive-approachroundaboutarefarmorecrowdedandcongested.Therefore,itismuchmoredifficulttoeliminatetheweavingandmergingthecongestionbytrafficsignalcontrols.Thefollowingthreereasonsmayaccountforthisdifficulty:
Firstly,themeaningsofturn-leftandgo-throughmakerlinesforfive-approachroundaboutsarenotthatclearastheonesoffour-approachroundabouts.Sothedriverscouldgetconfusedwhenchoosingroadwayaccordingtotheirdestinationandavoidweavingormerging;
Secondly,sincethattherearefivestoplinesinthefive-approachcirculatoryroadways,itismorelikelythatthevehiclesenteringtheroundaboutwouldstopforthreetimesbecauseofthecirculatoryroadwaysignals(Hydén&Várhelyi,2000);
Thirdly,withthesamecenterislandradius,thecirculatorycapacityoffive-approachroundaboutissmallerthanthatofthefour-approachone,andthesignalcycletimeislonger.Sothecirculatoryroadwaycapacityissupposedtobelargertoholdtheleft-turnflows.Anditisthereforemorecomplicatedtosetthecoordinativephasesbetweenthesignalsintheapproaches,theapproachesandcirculatoryroadwaysandinthecirculatoryroadways.
2.Methodology
2.1Aspecialconsiderationforsignalphasessetting
Appropriatesignalphasessettingcanpartlysolvetheconflictandweavingsituationbytheinandoutroundaboutflows.Basedontheconsiderationoftheroundaboutspaceresourceandtrafficflowvolumeofdifferentdirections,thesignalphasesdesignisexpectedtocoordinatetheweavingandconflictingincirculatoryroadways,assignthepassingrighttodifferentflowsreasonablyandreducethegreensignaltimingtoavoidathirdstoppinginthecirculatoryroadway.
Inthispaper,wesettherulethatthenumberingofapproachesiscounterclockwise(CCW),asisshowninFig1.Thetrafficflowthatentersfromapproachiandgetsoutthroughapproachjismarkedasflowij.AndthesignalsthatcontrolthepassingrightofthetrafficflowsinapproachesandinthecirculatoryroadwaysarealsonumberedinCCW,whichareconsistentwiththenumberingofthecorrespondentapproaches.
Fig.1Geometricdesignofatypicalfive-approachroundabout
2.2TheCycleLengthCOfTrafficLights
ThispartwewillcalculatethecyclelengthCoftrafficlights,thetimethelightusetogothroughallthecolour.TheremanymethodlikeF-B,HCM200andAustrliaARRB.Butmostofthisareusedincrossroads.Wethinkofthewaybeingsuitableforourmodelandconvenienttocalculate.AtlastwechoosetheWebsterequationtocalculatethetime.
Thesaturatedflowperlane:
weneedknowthesaturatedflowS,commonlywegiveacertainvalue.Andthisvalueisdifferentamongthelaneinwhichcarwillturntoright,leftorstraight.Sometimes,wewillcorrectionthisvalue.
Therateofflow
:
therateisthenumberofcaractuallycomeinphasei(werecorded)
dividethesaturatedinphasei
.
Thesumofthemaximumrateofflowindifferentphase:
Yisthesumofthemaximum
indifferentphases.
Thebestcyclelengthoftraffic
:
WeusetheWebsterequationtocalculate
.
WhereListhetotallosttimepercycle.
Where
isthelosttimecarusedtostart.Actuallymanyarticlethinkthistimeisabout3seconds.
isthetimebetweentwogreenlights.Itequalstothetimeofyellowlightsaddthetimeofredlights.
isthetimeofyellowlights.
2.3Roundaboutcapacityconstraints
Inthispaper,forafive-legroundabout,roundaboutcapacityhastwoformsaccordingtothedifferencesofroundabout’sspace.Thefirstoneisthequantityofvehiclesbetweentwoadjacentstoplinesonthecirculatoryroadwaywithinonecycle;thesecondoneisthequantityofvehiclesbetweenthestoplineonthecirculatoryroadwayandthestoplineontheentrancewithinonecycle.Whenwetrytooptimizethefive-legroundabout’ssignalcycle,thelengthofthecyclemustsatisfytheconstraintsofthequantityofthevehiclesintheroundaboutwithinonecycle.Ifinonecycle,thequeueintheroundaboutexceedstheroundabout’scapacity,thenthequeuewillspilltotheupstreamcircuit,whichmakesthevehiclesinthenextphraseunabletogetout.Thedeadlockphenomenonappeared.
Fig.2thecapacityoffive-approachroundabout
Inthispaper,thetwokinddefinitionsofcircuitmeanstwodifferentspaceelementstocalculatethecapacityofcircuit.Inthepicture2,thecurveABCmeansthetrackwhenthevehicledrivesfromtheentrancestoplinetothenextcirculatorystopline.AB’scentralangleisT,AB’sradiusisr,andBC’scentralangleisU,BC’sradiusisR.ThecurveDEmeansthetrackoftwoadjacentcirculatorystoplines.DE’scentralangleisVanditsradiusisR.Assumetheaveragestoplengthisl,thenABC’scapacityis:
Inthisformula,
meansthequantityofvehiclesintheavailablespaceforqueueofABC.DE’scapacityis:
Inthisformula,
meansthequantityofvehiclesintheavailablespaceforqueueofDE.
2.4Signalcoordinatecontrolmodeandcalculationofthedifferencevalueinphrase
Thefive-legroundaboutisusuallyrelativelybig,sowecancoordinatewiththedifferencesbetweenentrancessignals,betweencirculatorysignalsandbetweenentrancessignalsandcirculatorysignalstoreducethelosttimefromdifferentflowdirectionsanddifferentphrasesandtoimprovethefive-legroundabout’strafficcapacityasmuchaspossible.Inordertomakethevehicleswhichhaveenteredtheentrancegetoutoftheroundaboutassoonaspossibleandtostopaslessaspossible,thecirculatorysignalsshouldkeepgreenasmuchaspossibletoincreasetheproportionofkeep-goingtime.
coordinatethecirculatorysignalsandtheentrancesignals
Therearetwokindofsituationsthatneedstocoordinatesthecirculatorysignalsandtheentrancesignals:
①usethephrasedifferenceswhichareformedfromthespacedistancesbetweentheentrancestoplinesandthecirculatorystoplinestoincreasequeue’sdischargetimeincircuit.Becausethetimethatthequeuewaitingbeforethecirculatorystoplineusetoreachestheconflictpointofthequeueitselfandtheentrancevehiclesflowisalmostzero,wecanpostponethechangeofthegreensignalofcirculatoryvehicleflow.②meanwhile,thefive-legroundaboutshouldcareabouttheentrancesignalsandtheadjancentcirculatorysignalinthevehicles’forwarddirectiontoguaranteethatbeforetheentrancesignalturnsred,thevehiclesthathavepassedthestoplinecansuccessfullypasstheadjacentcirculatorystoplineinthevehicles